The deal with Iran falls far short of what the United States and its European allies would like. They wanted Tehran to dismantle its nuclear program, agree to unimpeded inspections, and forgo ballistic missiles and support of Hezbollah and Hamas. But these are terms that can only be imposed on a country that has been militarily defeated. So the two pertinent questions are whether the P5+1 got the best deal possible and, more importantly, whether it is better than the likely results of walking away from the table.

It is extremely unlikely that the P5+1 got the best deal possible (as disconcerting as that may be for proponents of the deal, including me). Part of the reason is that, as the critics have alleged, U.S. President Barack Obama wanted the agreement very badly, which—although necessary to undertake the arduous negotiations—did reduce his leverage. A more important point is that it is extremely rare for one side, let alone both, to get everything that it could. In almost all cases, the two sides’ preferences do not meet at a single point, but instead have some overlap, which means that it would take extraordinary intelligence and luck for either side to be able to squeeze out the last drop from the other.

Leonhard Foeger / Reuters

German Foreign Minister Frank Walter Steinmeier, High Representative of the European Union for Foreign Affairs and Security Policy Federica Mogherini, Iranian Foreign Minister Mohammad Javad Zarif, British Foreign Secretary Philip Hammond, and U.S. Secretary of State John Kerry arrive for a family picture after the last plenary session at the United Nations building in Vienna, Austria July 14, 2015.

Although the question of whether the West could have gotten a bit more in the bargain is interesting, much more important is the question of whether the deal was better than a breakdown of negotiations. It was, and by quite a wide margin.

Iran could still pursue a bomb. It could renounce or simply break the agreement, expel the inspectors, and use the declared facilities to produce highly enriched uranium. This has received the majority of attention in the media, but most experts believe it is the least likely route to a bomb because it invites an immediate attack. Alternatively, Tehran could also take a series of small steps, some cloaked in either secrecy or spurious justifications, toward